A preliminary study conducted primarily in laboratory mice indicates that breast cancer cells metastasize more readily when the animals have low levels of vitamin D. The researchers, including pediatric endocrinologist Brian Feldman, MD, PhD, and graduate student Jasmaine Williams and postdoctoral scholar Abhishek Aggarwal, PhD, found that vitamin D directly promotes the expression of a protein called ID1 known to be involved in metastasis of cancer cells. Their research was published today in Endocrinology.

The finding builds upon several previous studies suggesting that low levels of vitamin D not only increase a person’s risk of developing breast cancer, but are also correlated with more-aggressive tumors and worse prognoses. Although the research was conducted primarily in mice and on mouse cells, the researchers found in a study of 34 breast cancer patients that levels of circulating vitamin D were inversely correlated with the expression levels of ID1 protein in their tumors, and they confirmed that a vitamin D metabolite directly controls the expression of the ID1 gene in a human breast cancer cell line.

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"Although much more research needs to be done, research from our lab and others suggests that people at risk for breast cancer should know their vitamin D levels and take steps to correct any deficiencies," said [Feldman].

Feldman and his colleagues include a cautionary note, however:

The researchers emphasize that their findings don’t imply that more vitamin D is always better. Correcting a deficiency is very different from taking more than the recommended dosage, which the Institute of Medicine says is 600 international units per day for people age 70 and younger, and 800 IU for older adults. Excess levels, variously estimated to occur at about 4,000 to 10,000 IU per day, have been linked to damage to the kidneys, cardiovascular system and other organs.

The scenario many of us learned in school is that two X chromosomes make someone female, and an X and a Y chromosome make someone male. These are simplistic ways of thinking about what is scientifically very complex.